A new study of ancient ash suggests that the dormant giant could develop the conditions needed to blow in a span of mere decades.

After analyzing minerals in fossilized ash from the most recent mega-eruption, researchers at Arizona State University think the supervolcano last woke up after two influxes of fresh magma flowed into the reservoir below the caldera. And in an unsettling twist, the minerals revealed that the critical changes in temperature and composition built up in a matter of decades. Until now, geologists had thought it would take centuries for the supervolcano to make that transition.